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Effect of Mixture Design on Densification

Louay Mohammad

Louisiana Asphalt Technology ConferenceFebruary 23-24, 2005

Shreveport, Louisiana

2

Outline

- Background

- Objective

- Scope

- Mixtures Evaluation

- Results

- Concluding Remarks

3

Objectives of Mix DesignObjectives of Mix Design

• Resist– permanent deformation.– fatigue cracking – repeated load– low temperature cracking– moisture induced damage

• Resist skid• Workability

4

Steps Involved in the Mixture Design

1. Materials Selection1. Materials Selection 2. Design Aggregate Structure2. Design Aggregate Structure

3. Design Binder Content3. Design Binder Content 4. Moisture Sensitivity4. Moisture Sensitivity

TSRTSR

5

Superpave Mixture DesignConcerns:• Minimum VMA Criteria• Difficulties• Differentiate sound from

unsound mixtures• higher VMA mixtures

• Cannot guarantee• Durable• rut resistant

airairasphaltasphalt

aggagg

VOLVOL MASSMASS

VVTT

VMAVMA VVEACEAC

VVVV

6

Superpave Mixture DesignConcerns:• Aggregate Properties/Gradation

selection• 95 percent• Aggregate Specification

• Consensus – ETG• Little research• Aggregate Structure/Mixture Design

and Performance

7

Superpave Mixture DesignImprovement:• Design Aggregate Structure

• Mixture stability• Rational approach to design aggregate

structure • based on principles of aggregate packing

concepts

8

Objective

• Critically examine Superpave mixture design criterion

• Effect of – NMS – Aggregate Gradation and type

9

Scope• Aggregate Types

– Two `• Sandstone, Limestone

• Aggregate Structure– 12.5 mm NMS– 25 mm NMS

• Aggregate gradation– Coarse, Medium, Fine– Bailey Method

• analytical method that enables blending aggregates using engineering principles and packing theory concepts

10

Scope• Compaction Level

– 125 gyrations• Binder Type

– PG 76 – 22M

11

Methodology• Superpave Gyratory Compactor

– Densification Indices, Slope– Locking Point

• Pressure Distribution Analyzer – Frictional Indices, Locking

• Loaded Wheel Tester– PMW

K J I H G F E K J I H G F E D C B A D C B A

Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power

100100

00

% P

assi

ng%

Pas

sing

Combined Blend GradationCombined Blend Gradation

5050

2020

8080

Sieve % PassingA 100B 97C 76D 63E 39F 25G 17H 11I 7J 5K 4.2

1010

3030

4040

6060

7070

9090

CoarseFine

1

2

34

K J I H G F E K J I H G F E D C B A D C B A

Sieve Size (mm) Raised to 0.45 PowerSieve Size (mm) Raised to 0.45 Power

100100

00

% P

assi

ng%

Pas

sing

Combined Blend GradationCombined Blend Gradation

5050

2020

8080

Sieve % PassingA 100B 98C 85D 72E 58F 40G 32H 21I 12J 7K 4.4

1010

3030

4040

6060

7070

9090

1

2

3

4

CoarseFine

14

Aggregate Gradation ½ SS3/4"

1/2"

3/8"

No. 4

No. 8

No. 16

No. 30

No. 50

No. 100

No. 200

Sieve Size

0

10

20

30

40

50

60

70

80

90

100

Perc

ent P

assing

15

Aggregate Gradation 1” LS1.5"

1"3/4"

1/2"

3/8"

No. 4

No. 8

No. 16

No. 30

No. 50

No. 100

No. 200

Sieve Size

0

10

20

30

40

50

60

70

80

90

100

Per

cent

Pas

sing

Mixture Design

11.19.6 10

12

11.1 11.3

9.1

1413.1

8.4 8.5

14

02468

1012141618

1 LS 0.5 LS 0.5 SS

Coarse Medium Fine Specs63.5

58.2 60.5 64.8 62.758.5

69

50 54

0

20

40

60

80

VFA

1 LS 0.5 LS 0.5 SS

Coarse Medium Fine

3.8

3.0 3.3

5.1

4.0

3.5

5.1

3.6

3.9

0.0

2.0

4.0

6.0

%A

C

1 LS 0.5 LS 0.5 SS

Coarse Medium Fine8 5 . 78 9 .3 8 9 .5 89

8 5 . 1 8 6 . 28 8 89 8 6 . 6 8 6 .4 8 8 89

0

20

40

60

80

100

%G

mm

, Ni

1 LS 0.5 LS 0.5 SS

1775

80

85

90

95

100

0 30 60 90 120 150 180 210

No. Of Gyration

Ht,

mm

SGC

Pressure Distribution Analyzer

12

17

22

0 100 200 300No. of Gyrations

FR, p

siCoarseMediumFine

18

Superpave Gyratory CompactorLocking Point– Number of gyration

• Ht specimen remains constant for three consecutive gyrations

115.4

77

115.4115.4115.5115.5115.6115.6115.7115.7Height, mm

7675747372717069N0. Gyrations

75

80

85

90

95

100

0 30 60 90 120 150 180 210

No. Of Gyration

Ht,

mm

19

115.4

77

115.4115.4115.5115.5115.6115.6115.7115.7Height, mm

7675747372717069N0. Gyrations

Locking Point

Superpave Gyratory CompactorLocking Point

20

80828486889092949698

0.1 1 10 100 1000

No. of Gyrations

% G

mm

% @ % @( ) ( )

Gmm Ndes Gmm NiniLog Ndes Log Nini

−−

Superpave Gyratory CompactorSlope

21

75

80

85

90

95

100

0 50 100 150 200

No. of Gyrations

% G

mm

92%

N=1

CDI

Compaction Densification Index

N=205

TDI

Traffic Densification Index

Superpave Gyratory CompactorCompaction Indices

22

Pressure Distribution Analyzer

• Measures the frictional resistance of mixtures during compaction

• Double plate assembly with 3 load cells equally spaced on the perimeter

23100

300

500

700

900

1100

0 50 100 150 200 250 300

LC1 LC2 LC3

Pressure Distribution Analyzer

24

12

17

22

0 100 200 300No. of Gyrations

FR, p

si

CoarseMediumFine

Pressure Distribution AnalyzerFrictional Resistance

25

Rate of Change of Frictional Resistance

-0.10

0.10.20.30.40.50.6

0 50 100 150 200 250 300

No. of Gyrations

Rate o

f Chan

ge of F

R

-Maximum interlock in the aggregate structure

Number of gyrations corresponding to the point of minimum rate of change in FR

FR Locking Point

- 5

10

15

20

25

0 100 200 300No. of Gyrations

FR, p

si

Coarse Medium Fine

Pressure Distribution AnalyzerLocking Point

26

0

5

10

15

20

25

0 50 100 150 200 250 300

No of Gyrations

Fric

tiona

l Res

ista

nce,

psi

N=1 N@FR Locking Point

Compaction Force Index

200 gyrations

Traffic Force Index

Pressure Distribution AnalyzerIndices

27

Loaded Wheel Tracking Test

28

Four parameters (indices) are measured from the data collected in the HWT test- Post Compaction Consolidation - Inverse Creep Slope

- Stripping Inflection Point

- Stripping Slope

Loaded Wheel Tracking Test

29

020406080

100120140

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS FSpec

Superpave Gyratory CompactorLocking Point

30

0102030405060708090

100

% o

f Nde

s

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C

1" LS M

1" LS F

Superpave Gyratory CompactorLocking Point

31

0123456789

10

1/2"LS C1/2"LS M1/2"LS

1/2" SST C1/2" SST M1/2" SST 1"LS C

1" LS M

1" LS F

Superpave Gyratory CompactorCompaction Slope

32

050

100150200250300350400

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

Superpave Gyratory CompactorCompaction Indices -- CDI

33

0100200300400500600700800

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

Superpave Gyratory CompactorCompaction Indices -- TDI

34

020406080

100120140

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

Ndes=125

Pressure Distribution AnalyzerFR Locking Point

35

68.860

52.8

67.2 62.456.8

68.8

46.4 46.4

0

20

40

60

80

100%

of N

des

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

Pressure Distribution AnalyzerFR Locking Point

36

Frictional Resistance – Locking Point

0

5

10

15

20

FR, p

si

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS FUSB190 BC

37

0

400

800

1200

1600

2000

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

Pressure Distribution AnalyzerFR -- CFI

38

0

1000

2000

3000

4000

5000

1/2"LS C

1/2"LS M

1/2"LS F

1/2" SST C

1/2" SST M

1/2" SST F

1"LS C

1" LS M

1" LS F

Pressure Distribution AnalyzerFR -- DFI

39

Relationship: No. of Gyrations SGC LP vs. PDA LP

y = 1.0x - 4.0R2 = 0.95

40

50

60

70

80

90

100

40 50 60 70 80 90 100

SGC Locking Point

FR L

ocki

ng P

oint

40

y = 0.70x + 1.65R2 = 0.71

4.6

4.8

5

5.2

5.4

5.6

4.6 4.8 5 5.2 5.4 5.6

VTM at SGC Locking Point, %

VT

M a

t FR

Loc

king

Poi

nt, %

Relationship: VTM SGC LP vs. PDA LP

41

0

100

200

300

400

4 6 8 10 12 14

VMA

CD

I

0

200

400

600

800

4 6 8 10 12 14

VMA

TD

I

Relationship: VMA vs SGC CDI & TDI

• Trends• Increase VMA

• Higher CDI• Lower TDI

• Is there a Min. VMA?

42

R2 = 0.91

600

800

1000

1200

1400

1600

1800

0 100 200 300 400

CDI

CFI

Relationship: Compaction IndicesSGC CDI vs PDA CFI

43

R2 = 0.19

2500

3500

4500

400 600 800

TDI

TFI

Relationship: Compaction IndicesSGC TDI vs PDA TFI

44

R2 = 0.90

800

1000

1200

1400

1600

1800

4 6 8 10 12

Compaction Slope

CFI

Relationship: SCG Compaction Slope vs. CFI

45

LWT Test Results

0

1

2

3

4

5

1/2"LS C1/2"LS M1/2"LS F1/2" SST C1/2" SST M1/2" SST F1"LS C1" LS M1" LS F

46

012345

0 100 200 300 400

CDI

HWT

Rut, m

m

012345

1000 1100 1200 1300 1400 1500 1600 1700 1800

CFI

HW

T R

ut, m

m

Relationship: Rut Dept vs. CDI & CFI

47

012345

400 500 600 700 800

TDI

HWT R

ut, m

m

012345

3600 3700 3800 3900 4000 4100 4200 4300 4400 4500 4600 4700

TFI

HWT

Rut,

mm

Relationship: Rut Dept vs. TDI & TFI

48

Relationship: Rut Depth vs. FR

00.5

11.5

22.5

33.5

44.5

5

20 20.5 21 21.5 22 22.5 23

FR at Locking Point, psi

HW

T R

ut D

epth

, mm

49

R2 = 0.73

00.5

11.5

22.5

33.5

44.5

5

2 4 6 8 10 12

Compaction Slope

HW

T R

ut, m

m

Relationship: LWT Rut Depth & Compaction Slope

50

Conclusions- SGC densification curves can provide valuable information

about mixtures behavior during compaction- CDI, Slope

• Coarse-grades mixtures had higher SGC LP– 50% - 70% of Ndesign

• Coarse-grades mixtures had higher Compaction Slope:– 6-10

• SGC CDI and PDA CFI indices were higher for Coarse-grades mixtures

• PDA measured LP showed similar ranking as SGC LP– Lower

• FR increased with an increased in the NMS

51

Conclusions

• Good correlation was observed B/W – SGC LP and PDA LP– SGC CDI and PDA CFI– SGC Slope and CDI– SGC Slope and LWT rut depth

• Poor correlation was observed B/W – SGC TDI and PDA TFI

• Mixtures evaluated performed well in the LWT

52

Thank You